I use the "Commander" type interface. In Total Commander it's works "normaly".
Providing you use default configuration (Explorer-style selection = Mouse only), this is expected behaviour.
The mouse click selects the file (Explorer-style selection), the Insert key deselect the file. Supposing you are on Windows 7/8, the mouse hovering on the file creates selection effect (that's Windows 7/8 behaviour). Only after you more mouse out of the file, the true de-selected state can be seen.
If you click with mouse on a file row, and after you press 'Insert' key, the row will not be selected.
It's shows as selected, but if you move mouse out of the row, there is no selection.
Version: 5.1.4
Regards,
Ferenc